Two vaccines effective against bird flu
Two of the four vaccines tested for their efficacy against HPAI (highly pathogenic avian influenza) type H5N1 bird flu are effective under laboratory conditions. "The so-called HVT-H5 vaccines offer protection against disease symptoms in laying hens and prevent the spread of the virus," said Nancy Beerens, head of the National Reference Laboratory for avian influenza.
The vaccine study was carried out at Wageningen Bioveterinary Research, part of Wageningen University & Research (WUR), in collaboration with Utrecht University, Royal GD and WUR, on behalf of the Dutch Ministry of Agriculture, Nature and Food Quality (LNV).
In the study, three modern vaccines were tested in laying hens. These were:
- HVT-H5 vaccine from Ceva Sante Animale
- HVT-H5 vaccine from Boehringer Ingelheim Animal Health
- DNA-vaccine from Huvepharma
In addition, the Nobilis vaccine of Merck Sharp & Dome was included in the study. This is an older type of vaccine and is the only vaccine currently registered as a two-dose vaccine in the Netherlands. The effectiveness of the Nobilis vaccine against the current bird flu virus has not been tested before. In this study all vaccines were applied as a single dose.
"An important selection criterium for the candidate vaccines is the possibility to distinguish between animals that have been vaccinated and animals that produce antibodies due to a bird flu infection. With the three modern vaccines, this distinction can be made; they comply with the so-called DIVA principle," explains Nancy Beerens. The selected vaccines are already on the market in other countries, or at an advanced stage of development. However, whether these vaccines are effective in preventing disease after infection with the current HPAI H5N1 virus found in Europe and can prevent the spread of the virus between laying hens was not tested before.
Each vaccine was administered to ten laying hens. Subsequently, five chickens were infected with the bird flu virus. These were grouped together with the five chickens that were not infected. This study design investigated whether the virus would spread from infected chickens to uninfected chickens.
Both HVT-H5 vaccines have been found to be 100% effective in preventing disease and mortality after infection with the HPAI H5N1 virus. This is in contrast to the other two vaccines in which disease was observed. The study showed that both HVT-H5 vaccines prevent virus spread between chickens. For both these vaccines, the calculated reproduction ratio (R-value) was significantly lower than 1. Also, both the reproduction ratios of these two vaccinated groups differed significantly from the control group. The single dose of Nobilis vaccine prevents virus transmission in one of the two groups, but this difference was not significant compared to the control group.
"Our study shows that both HVT-H5 vaccines are effective under laboratory conditions and prevent both disease and virus spread. These vaccines comply with the DIVA principle and are therefore good candidates for further research in practice," says Beerens. HVT-H5 vaccines can be administered in the egg or to day-old chicks in the hatchery.
The results of the conducted study cannot be extrapolated to the field. "It is important to investigate whether the vaccines work well under field conditions in poultry farms, how long the vaccines protect, and whether one vaccination is sufficient." The Dutch Ministry of LNV has commissioned a field study that will start this summer.
In addition, the vaccines still have to be registered in the Netherlands and the European Union. "There are still some hurdles to overcome, but the results of our research are an important first step towards vaccination against the bird flu virus in poultry," says Beerens.